[Question] I'm curious about how to resolve the pain in my right shoulder blade that I get from washing my hair.

This morning, while washing my hair, I suddenly felt pain near my right shoulder blade.
I felt a stiff sensation immediately after lifting my arm to wash my hair, and the pain has persisted.
I'm not sure if it's just simple muscle stiffness or if there's another cause.
I put on a patch, but the pain gets a bit worse when I move my shoulder.
What should I do to relieve the pain?
Are there any helpful stretches?